This invention relates to a current detector for detection or measurement of electric current flowing in an electric circuit, and more specifically to such a detector incorporating a Hall-effect device more generally known also as Hall generator.
The Hall generator is built upon the familiar Hall effect to develop a voltage, known as Hall voltage, in proportion to the strength of the magnetic field applied. Positioned contiguous to a path of electric current, the Hall generator will put out a voltage indicative of the magnitude of the current by being acted upon by the magnetic field appearing in proportion to the current magnitude.
A variety of contrivances have been suggested and incorporated with Hall-effect current detectors for enhancing the sensitivity of current detection by the Hall generators. Japanese Unexamined Patent Publication No. 4-364472 represents one such conventional effort, perhaps bearing the most pertinence to the instant invention. It teaches use of a core of high magnetic permeability embracing the current path in order to cause the magnetic lines of force due to the current flowing through the path, to act effectively upon the Hall generator.
Although capable of well achieving the objective for which it is designed, this prior art device is not totally satisfactory. The magnetic core is inconveniently bulky and expensive, adding substantively to the size and manufacturing cost of the current detector.
The present invention aims at improvement of the sensitivity of the current detector of the kind defined, without the noted shortcomings of the closest prior art.
Stated in brief, the invention concerns a current detector utilizing the Hall-effect for detection or measurement of electric current, comprising a current-path conductor for carrying current to be detected or measured, and a Hall generator disposed in prescribed positional relationship to the current-path conductor for generating a Hall voltage proportional to the strength of a magnetic field due to the current flowing through the current-path conductor. The invention particularly features a magnetic overlay in the form of a sheet or film of magnetic material covering prescribed part of the current-path conductor.
Formed on the current-path conductor to a thickness much less than that of this conductor, the magnetic overlay functions to confine the magnetic lines of force due to current flow through the current-path conductor and hence to enhance the flux density acting effectively on the Hall generator. The sensitivity of the current detector is thus improved by far more inexpensive and compact means than the conventional magnetic core.
In a representative embodiment of the invention the current-path conductor takes the form of a piece of sheet metal with a slit cut therein to provide a U-shaped path for the flow of the current to be detected or measured. Such a piece of sheet metal is easy to fabricate, as by the punching of nickel-plated sheet copper, So fabricated, the sheet-metal current-path conductor has a pair of opposite major surfaces, an inside surface contiguous to the slit, and an outside surface facing away from the slit. The Hall generator together with associated electronics is fabricated in the form of an integrated circuit, which is held opposite one of the major surfaces of the current-path conductor and, as seen in a direction normal to this conductor, contained in the slit therein. The magnetic overlay is formed on the current-path conductor, covering at least either, preferably both, of the other major surface and outside surface of the current-path conductor.
Such an overlay can be readily formed as by plating preselected part of the current-path conductor with a magnetic material such as Permalloy, by bonding a preformed sheet or film of such material, or by vaporization, pressure welding, or deposition of such material.
For still higher detection sensitivity, magnetic overlays may be formed on some additional parts of the current detector other than the current path conductor. Such additional parts include a baseplate on which is formed the integrated Hall generator circuit, and a casing enveloping the Hall generator circuit and part of the current-path conductor.
The above and other objects, features and advantages of this invention will become more apparent, and the invention itself will best be understood, from a study of the following description and appended claims, with reference had to the attached drawings showing the preferred embodiments of the invention.